Magnetic imaging of domain walls in the antiferromagnetic topological insulator MnBi2Te4.

The control of domain walls or spin textures is crucial for spintronic applications of antiferromagnets. Despite many efforts, it has been challenging to directly visualize antiferromagnetic domains or domain walls with nanoscale resolution, especially in magnetic field. Here, we report magnetic imaging of domain walls in several uniaxial antiferromagnets, the topological insulator MnBi2Te4 family, using cryogenic magnetic force microscopy (MFM). Our MFM results reveal higher magnetic susceptibility inside the domain walls than in domains. Domain walls in these antiferromagnets form randomly with strong thermal and magnetic field dependence. The direct visualization of these domain walls and domain structures in magnetic field will not only facilitate the exploration of intrinsic topological phenomena in antiferromagnetic topological insulators, but will also open a new path toward control and manipulation of domain walls or spin textures in functional antiferromagnets.